The focus of this section is on the discovery and functional analysis of the network of genes involved in the development and operation of the nervous system. Two transcription factors of the kruppel class of the zinc finger superfamily, rKr1 and rKr2, have recently been cloned. The recognition sites to which rKr1 and rKr2 bind in vivo are being assessed in a yeast one-hybrid system; the function of these zinc finger proteins is also being investigated through the construction of a dominant negative version of rKr2 in transgenic mice. Identifying the set of target genes that each of these zinc finger proteins recognizes is the first step in characterizing a genetic network. Cell culture systems are an invaluable tool in neural cell biology, but the difficulties in obtaining purified populations of neural cells has limited some studies. We have developed a transgenic mouse strategy for isolating pure populations of oligodendrocytes and their progenitors. Several transgenic mouse lines were created in which a myelin gene promoter drives expression of a geo reporter, thus enabling an antibiotic selection for oligodendrocytes from mouse brain. The surviving oligodendrocytes can also be distinguished from other cell types by their expression of the lacZ gene. Ongoing experiments are aimed at optimizing the selective conditions for culturing oligodendrocytes corresponding to various developmental stages.